GNU bug report logs - #25166
It shouldn't be possible to set the function cell of t

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From: Philipp Stephani <p.stephani2 <at> gmail.com>
To: Glenn Morris <rgm <at> gnu.org>
Cc: 25166 <at> debbugs.gnu.org
Subject: bug#25166: 26.0.50; It shouldn't be possible to set the function cell of nil and t
Date: Mon, 26 Dec 2016 19:41:00 +0000

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Philipp Stephani <p.stephani2 <at> gmail.com> schrieb am Mo., 26. Dez. 2016 um
20:29 Uhr:

> Glenn Morris <rgm <at> gnu.org> schrieb am Mo., 12. Dez. 2016 um 21:25 Uhr:
>
> Glenn Morris wrote:
>
> > Philipp wrote:
> >
> >> You can set the function cell of nil and t using `fset' and friends.
> >> But you can't call the `nil' function using (nil) (it does work with
> >> (t)).  I think that attempting to set the function cell of nil and t is
> >> almost always a bug -- probably the programmer wanted to set a real
> >> symbol, but some of the constants got passed.  I propose to signal an
> >> error (e.g. `setting-constant') whenever the function cell of nil and t
> >> is modified; maybe the same should happen for keywords.
> >
> > I just did this yesterday...
> > See https://debbugs.gnu.org/25110, ba8e883, and 3fd4433.
>
> And now see also ffb1302. :)
> Anyway, I only did "nil", since as you say "t" can actually be called as
> a function. But you are right that it's probably unintended.
>
>
> Thanks! Interestingly the behavior was already added in 1994 (commit
> c15c5d408d696928862ca2848a359231e373556c), but apparently reverted later.
> I'd suggest to simply reinstate that commit.
>

Here's a patch.

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[0001-Prevent-setting-the-function-cell-of-t-Bug-25166.txt (text/plain, attachment)]

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